A synergistic application of simultaneous electrocoagulation-electrooxidation process for the treatment of floor-wash wastewater containing Rhodamine B dye

Floor-wash wastewater (FWW) generated from dye manufacturing plants is a voluminous stream containing high colour and low COD. Such streams can be treated separately, and reused for floor-washing. In the present study, FWW containing Rhodamine B (RhB) dye was treated using a simultaneous electrocoagulation-electrooxidation (EC-EO) system with a precisely controlled energy supply to EC and EO. Compared to only EC or only EO, the ECEO system achieved significantly greater COD and colour removal from FWW. With a total charge of 0.63 Ah/L evenly distributed between EC and EO, the colour and COD removal were similar to 100 and 94.43 %, respectively. The formation of insoluble, polymerized products in EO and their subsequent entrapment in metal hydroxide flocs formed in EC was the main pathway for RhB removal from FWW. The total energy and specific energy consumptions were: 1.66 kWh/m(3) and 5.22 Wh/g-COD removed for EC-50 %1EO-50 %; 2.82 kWh/m(3) and 11.45 Wh/g-COD removed for EC-00 %1EO-100 %; and 1.75 kWh/m(3) and 40.23 Wh/g-COD removed for EC-100 %1EO00 %, respectively, indicating significant synergy between EC and EO processes applied simultaneously. FTIR and LC-MS analyses were performed to delineate the degradation pathway of RhB. The seed germination test was performed using treated FWW to assess toxicity. Seeds exposed to EC-EO-treated FWW had no significant adverse effect on soot and root length, while delayed seed germination was observed in seedlings exposed to raw FWW. This work presents a previously unreported mechanism of RhB removal by simultaneous EC-EO process.

Automated summary

In this study, FWW containing Rhodamine B dye was effectively treated using a simultaneous EC-EO system, achieving high removal of COD and colour. The main pathway for RhB removal was the formation of insoluble, polymerized products in EO and their subsequent entrapment in metal hydroxide flocs formed in EC. The toxicity test showed low adverse effects on seed germination when exposed to treated FWW.